Crude oil and natural gas are produced from porous and permeable subterranean formations. The porosity or void space of the formation is a measure of the ability of a formation to store oil or gas. Permeability is a measure of the fluid conductivity of the formation. Permeability is related to the ability of fluids to move through the pores of the formation and is a necessary and essential requirement for the production of reservoir fluids. Where the natural permeability of a formation is low or operations within a well have damaged the ability of the formation to transmit fluids, the productivity of the well will be reduced. Remedial operations are necessary to increase the permeability in such cases.
Acidizing and fracturing are commonly employed methods for increasing the permeability of the formation. Both are methods for artificially creating channels of high fluid conductivity within the formation. Acidizing is accomplished by contacting the formation with an acid which will chemically react with and dissolve the formation. Acidization is often employed in conjunction with hydraulic fracturing.
Hydraulic fracturing is accomplished by subjecting a formation to high pressure fluid which is pumped down the well and into contact with the formation. This high pressure fluid causes the formation to split along lines of weakness when the yield strength of the formation is exceeded. These fractures are zones of high fluid conductivity and greatly increase the productivity of the formation.
When the pressure of the injected fluid is reduced, the fractures will tend to close due to the unbalanced compressive forces which are exerted on the formation. To prevent closure of the factures, propping agents are commonly employed. These propping agents are generally sand, metallic shot, plastic particles, glass beads, ceramics such as sintered bauxite, or woody material such as walnut hull fragments and are normally injected with a fracturing fluid to hold a fracture in an open position when fracturing pressure is relieved.
U.S. Pat. No. 3,481,401 to Graham describes a method of acidizing a fracture propped with a deformable acid resistant particle. This method creates channels of high fluid conductivity between columns of the formation rock which were insulated from acid attack by the deformable acid resistant proppant. Other patents, for example, U.S. Pat. No. 3,929,191 to Graham et al. disclose methods of propping fractures with self-consolidating resin coated particles. These methods, although effective, do not result in the same degree of increased productivity of the well as does the method of the present invention.